The GMC PM151 front turn signal requires a 1034, 1073, or 1129 bulb size, while the rear turn signal uses a 1073 or 1129 bulb size. The replacement chart covers 1955 to 1957 model production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC PM151 uses three distinct bulb types across its front and rear turn signal positions for the 1955-1957 model years: the 1034, 1073, and 1129.
Both the 1034 and 1129 are dual-filament bulbs rated at 12V and 21/5W, fitted with a BAY15d bayonet base, and classified as variants of the 1157 under the ANSI standard applicable in the US and Canada.
The 1073 is a single-filament bulb rated at 12V and 13W, fitted with a BA15s bayonet base, and classified as a lower wattage variant of the 1156 under the same ANSI standard.
A BAY15d base features two offset pins that prevent incorrect insertion, while a BA15s base uses a single pin, meaning the 1073 is physically incompatible with sockets designed for the 1034 or 1129.
The dual-filament design of the 1034 and 1129 allows a single bulb to serve two independent lighting functions, typically a brighter filament for the turn signal and a dimmer one for a secondary function such as a running light.
For the 1957 GMC PM151, the front turn signal uses the 1034 while the rear uses the 1073, meaning the front and rear sockets are not interchangeable due to differing base types and filament configurations.
The 1955 model year is the only year in which the same bulb type, the 1129, is specified for both the front and rear turn signal positions.
Although the 1034 and 1129 share identical electrical ratings and base types, they carry different ANSI designations and are listed as separate part numbers, which may indicate differences in filament positioning or light output distribution relevant to fitment.